Net Present Value problem

[spacecaptainsuperguy]

I'm trying to set up a "simple" calculator for a co-worker who sells memberships at a country club. The purpose of the calculator is to help show an individual why it makes financial sense to join now (mid-year) and have monthly dues waived for some number of months as opposed to waiting until December and joining right before the membership deposit goes up in January and be required to pay dues from day one.

I'm not exactly sure how to build an NPV formula for the 'join later' column (cell C11). The assumption I am using is that the prospective member would take his money and invest it at the assumed rate and then use those funds to join and pay dues at the later dates. I've got a formula in there right now, but it is only giving me their net out of pocket expense, not the net present value of those funds.

If it is easier for you, you are welcome to download the spreadsheet at:
http://www.4shared.com/dir/7676441/8cca2992/sharing.html
otherwise, here is what I have so far:

...and thanks in advance for any help.
SpaceCaptainSuperGuy

NPV Calculator.xls
	A	B	C	D
1	CurrentMembershipDeposit	27,500
2	ExpectedNewMembershipDeposit	30,000
3	CurrentMonthlyDues	360
4	ExpectedNewMonthlyDues	390
5	AssumedInterestRateEarned	8%
6	NoofMonthsDuesWaived	24
7	CurrentDate	7/29/2008
8	JoinLaterDate	12/31/2008
9
10		JoinNow	JoinLater
11
12	PresentValue	27,500	33,485
13
14	July-08	(27,500)	34,910	Interestearned
15	August-08	0	0	233
16	September-08	0	0	233
17	October-08	0	0	233
18	November-08	0	0	233
19	December-08	0	(27,500)	49
20	January-09	0	(390)	47
21	February-09	0	(390)	44
22	March-09	0	(390)	42
23	April-09	0	(390)	39
24	May-09	0	(390)	36
25	June-09	0	(390)	34
26	July-09	0	(390)	31
27	August-09	0	(390)	29
Sheet1

 

[spacecaptainsuperguy]

I did not know that. Very interesting. thank you for the follow up.